Further investigations of the sites of replication of EB virus found in oropharyngeal secretions confirm the importance of the salivary glands as a likely source. Parotid fluids obtained by cannulation of Stensen's duct has yielded EBV in two instances. The leukoviremia that is found in infectious mononucleosis has been examined quantitatively; T cell depleted populations of peripheral blood cells have a markedly increased transformation frequency, and higher transformation frequencies are found in large cell subpopulations. Comparison of 6 EBV strains by cross neutralization with hyperimmune "monospecific" rabbit antisera showed extensive cross reactions, indicating that there are shared antigens on the surface of the viruses. Absorption studies are in progress to determine whether EBV strains have unique antigens.